The use of wire to form magnetic coils is well known. Also, it is known that superconductive materials formed from certain alloys can be used to form devices such as magnetic coils, with such devices being limited, however, to use where the magnetic fields are relatively small (normally less than 8 Tesla).
It is likewise known that superconductive materials belonging to the A15 crystal structure class can be, and are, presently used in magnetic coils utilizing high current superconducting elements where magnetic fields greater than about 8 Tesla (T) are needed, or where an increased temperature margin for stability is needed.
While coils utilizing A15 superconductors have been successfully utilized, at least in some instances, it has been found that mechanical strain (compressive or tensile) severely degrades (decreases) the critical current and critical field of the superconductive materials. For example, in the most commonly used high magnetic field superconductive material (Nb.sub.3 Sn), an intrinsic tensile strain of only 0.5% has been found to produce approximately a 50% reversible decrease in the critical current at a magnetic field of 12T relative to the superconductive material's strain free critical current. It has been found that similar degradation of the critical current and critical field occurs with mechanical strain in other practical A15 superconductive materials, including Nb.sub.3 Sn, Nb-Hf/Cu-Sn-Ga, Nb-Ta/Cu-Sn, Nb-Ti/Cu-Sn, Nb.sub.3 Ge, Nb.sub.3 Al, and V.sub.3 Ga. The degradation is a consistent, reproducable and reversible function of the strain experienced by superconductive materials, and the relative magnitude of the degradation becomes greater the higher the magnetic field applied to the superconductor.
A superconductive wire that is stated to have improved strain characteristics formed from A15 crystal structure materials is shown in U.S. Pat. No. 4,324,842. While this wire is said to provide a better strain characteristic than was heretofore provided by known Nb.sub.3 Sn conductors, in order to prevent appreciable degradation of the critical current, the operating range must still be limited to a narrow strain range where the critical current is maximum. Also, as the magnetic field experienced by the superconductor is increased, the relative strain degradation of the critical current in the superconductive wire becomes much larger than that shown, which was measured at 4 T.
Forming a fiber, or wire, utilizing a superconductive material from the B1 crystal structure class has also been heretofore suggested (see, for example, U.S. Pat. Nos. 3,951,870 and 4,050,147 and United Kingdom Patent Application No. 2044737). Likewise, it has also been heretofore suggested that a superconductive wire made from materials in the B1 crystal structure class might be used to form a magnetic coil (see, for example, U.S. Pat. No. 3,951,870). Use of superconductive elements formed from the B1 crystal structure class have not, however, been heretofore suggested as a device for extending strain operating ranges in applications such as high field magnet systems, rotating machinery and/or transmission lines, for example.